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Thread: 3:55 gears or 3:73?

  1. #1
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    3:55 gears or 3:73?

    Hey guys I have done some searching around on here and can't really find any answers on weither you guys recommend 3:73 or 3:55 gears. It will be for street 90% strip 1% and highway 9% lol I don't know if I will notice the difference on any or those applications. I'm mainly looking to run close to 110-120 in a race at WOT not in OD cause I have a AOD tranny.

  2. #2
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    Quote Originally Posted by 90tbirdsc View Post
    Hey guys I have done some searching around on here and can't really find any answers on weither you guys recommend 3:73 or 3:55 gears. It will be for street 90% strip 1% and highway 9% lol I don't know if I will notice the difference on any or those applications. I'm mainly looking to run close to 110-120 in a race at WOT not in OD cause I have a AOD tranny.
    We can work the math backwards to tell you the maximum gear.

    Let's first assume, because it helps make the math easier, your redline is 6000 RPM, and that's what you want to hit 120MPH at.

    Given that 6000 RPM is 100 RPS, and 120MPH is 2 MPM or 1/30 MPS ...

    A stock 225/60R16 tire is nominally 26.60" diameter, 83.66" circumference.

    An AOD in 3rd gear is 1:1.

    Every second, your car will be travelling 1/30 mile, or approximately 176 feet. 176 feet is 2112 inches. Your tire will spin 25 times for that 1/30 mile. To get the tire to spin 25 times, while your engine spins 100 times, you'll need about a 4:1 ratio. So given all that, I'd opt for 3.73 rear gears. This will put you at about 5600 RPM at 120MPH.

    Please correct for your car's actual rear tire circumference, your actual redline, and your desired RPM at 120MPH *grins* But that's what the math says.

    RwP

  3. #3
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    Ok, I understand all of that. Now question #2. Any noticeable 1/4 time differences or street acceleration differences between 3:55 and 3:73 gears?

  4. #4
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    go 3.73 and enjoy the new acceleration. It makes the car feel like 500 lbs lighter.
    Scott Long
    1992 SC 5-speed
    Black on black leather, lowered, 18x9 Chrome Saleens...

  5. #5
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    yea i will agree with scott on that.wow

  6. #6
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    Well I already have 3:73 gears. I just need new ones. Any differences between traction with 3:73 or 3:55?

  7. #7
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    traction is going to depend on what rubber your running. my 245/45/17's have problems holding.lol

  8. #8
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    I'll be running 255/50-16 toyo proxes tq for serious street. Otherwise 225 high peformance summer tires. I don't care if it spins through 1st just as long as it hooks in second.

    In the spring I'll easily have about 70-80 more hp than I did in the fall and I could spin through 1st and half of second on 225 cheap tires with 3:73 gears.

  9. #9
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    Quote Originally Posted by 90tbirdsc View Post
    I'll be running 255/50-16 toyo proxes tq for serious street. Otherwise 225 high peformance summer tires. I don't care if it spins through 1st just as long as it hooks in second.

    In the spring I'll easily have about 70-80 more hp than I did in the fall and I could spin through 1st and half of second on 225 cheap tires with 3:73 gears.
    Nobody can answer your questions about how much it's going to spin with those street tires, there are just too many varibles. For the track you really need drag radials or slicks.

    If you want the best balance of gearing for street with ocassional track use, I agree with the people who have reccomended 3.73s. For best track performance use 4.10s and for the best gas milage leave the stock 3.27s in there. Nodody uses 3.55s with an AOD because there isn't enough differince between them and stock, to make it worth the effort/expense of doing the gear swap.

    3.73s will be fine on the track, so long as the tire is at least 26" diameter.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat...............707HP/650TQ

    My Garage

  10. #10
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    Ok thanks for the info

  11. #11
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    For a mostly street car, I'd go 3.55 with a wide ratio planet

  12. #12
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    It all depends on the tire size you are running on the street. I ran some rather large tires on my 18's and had 4:10's and also 3:73's at one time. Didnt bother me on the interstate in OD... Get to the track and swap on some track tires and there is where you will need to decide on 26 or 28 inch tire height... Might get lucky and get some 27's... Depends on what RPM you want to trap at the end of the track...
    Anthony Arnold
    Home of "No Cash Racing!"

    Silver 90 AOD 12.03 @ Shootout 2010
    White 94 Auto ??????
    Black 95 5-speed ????

  13. #13
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    Anthony, what gears do you have now in your silver rocket ship?
    Scott Long
    1992 SC 5-speed
    Black on black leather, lowered, 18x9 Chrome Saleens...

  14. #14
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    Deff go with 3.73 thats wat i am putting in my car and its a great street and strip gear.

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